I'll quote some of my favorite parts, paraphrased, of his second post on grading. His post is mostly written by Rick Wormeli.
Grades are first and foremost communication; they are information, nothing more. The moment we make them something more, we corrupt their constructive use. A reporting system built merely to sort humans in order to provide sports eligibility or grant scholarships is destined to be abused and unhelpful in the long term.
It's helpful to think of grades as the colored dot posted at our intended destination on a GPS system. (This analogy is thanks to Stan Williams and Emily Rinkema @CVULearns).